Even is not rising once after clicking Download report?

Below is my code:-

public void ExportToExcel()
        {
            DataTable dataTab = BindListItemToDataTable();
            if (dataTab.Rows.Count > 0)
            {
                string fileName = "ExportItems.xls";
                System.IO.StringWriter strWriter = new System.IO.StringWriter();
                System.Web.UI.HtmlTextWriter htmlWriter = new System.Web.UI.HtmlTextWriter(strWriter);
                DataGrid grid = new DataGrid();
                grid.DataSource = dataTab;
                grid.DataBind();
                grid.RenderControl(htmlWriter);
                Response.ContentType = "application/vnd.ms-excel";
                Response.AppendHeader("Content-Disposition", "attachment; filename=" + fileName + "");
                this.EnableViewState = false;
                Response.Write(strWriter.ToString());
                Response.End();
            }
        } 

When I click first time on Download button  It works fine, but again I  click on same button or any other button on the form then event not  riseing (Paused). Please help me out in this.

Thanks,

Vishwa